Since an appearance last Thursday on Winfrey's television talk show, books by Roizen and Oz have occupied the top three spots on the best seller list of Amazon.com, with customers buying both the book alone and the book and DVD of their new work, "YOU: On a Diet," and the hardcover edition of a previous text, "YOU: The Owner's Manual," a million seller in 2005 thanks in part to Winfrey.

"Oprah obviously has a passion for their work. It's very exciting," said Martha Levin, publisher of the Free Press, an imprint of Simon & Schuster that has increased the print run of "YOU: On a Diet," from 650,000 to 950,000.

Roizen and Oz specialize in easy-to-understand guides to healthy living, written with hip, simple language. The authors regard the human body as a house — the heart is the water main, the digestive system part of the plumbing and the bones the foundation.

Winfrey's support for Roizen and Oz is separate from her book club picks, which virtually guarantees hundreds of thousands of sales. Her last official selection was 10 months ago, when she chose Elie Wiesel's "Night," her longest hiatus since she suspended the club for a year in 2002-2003.

"It has been a long time," Levin told the AP on Sunday, "and publishers have been thinking about her club with nostalgia."